The present invention relates to permanent magnets. More particularly, the invention relates to a permanent magnet used in a rotor of an electric machine, and to a use of permanent magnets in the rotor of the electric machine.
A permanent magnet described in CH 549 307 A has the shape of a horseshoe wherein its yoke is innermost and its limbs are directed outwards. This permanent magnet does not necessarily have the external shape of a horseshoe, since the cited publication discloses that the magnet may be formed in the shape of a hexagonal or segment-type block. In addition to creating the U or V shape of the permanent magnet using individual rectangular permanent magnets, magnets having the shape of a U or V in a single piece are also described. The limbs of the magnet extend radially outwards, such that the two magnetic poles of the permanent magnet are located at circumferentially separate points on the outermost radial surface of the magnet. The magnets in that publication are made of a material having a high coercive force and may be a ceramic or metallic mass or a mixture of Iron powder that is bonded by rubber or resin. Permanent magnets are usually magnetized before assembly, but a stator winding may also be used for magnetizing them or setting a magnetization level.
In that publication, the permanent magnets are used in a permanent magnet rotor for alternating current machines, in particular synchronous motors or synchronous generators. The rotor preferably includes a squirrel-cage winding, which is already known, in order to provide the breakaway moment in a manner similar to the way in which it is provided in squirrel-cage motors. The permanent magnets and the rods can both be held in place by a cast aluminum body, if the rotor end ring of the squirrel-cage winding is an aluminum casting. An adhesive may be used to hold the magnets in place during the casting process. If the squirrel-cage rotor Is made of copper rods, the magnets can be held by the copper rods or a combination of the copper rods and an adhesive that attaches the magnets to the coil, e.g. epoxy resin.
It would be desirable and advantageous to address prior art shortcomings.